The objective of this project is to understand with greater clarity the role of calcium ion (Ca2 ion) in neuromuscular transmission. The end-plate potential (e.p.p.) is abolished in the absence of extracellular Ca2 ion, while the miniature end-plate potentials (m.e.p.p.'s) persist under the same conditions and are accelerated by non-depolarizing agents. In order to reconcile these aparently contradictory observations, the Ca2 ion-binding site is to be characterized, the effects of Ca 2 ion inside the terminal are to be examined, and the possible site of a large, inaccessible store of Ca2 ion within the terminal is to be sought for.